1. Field of the Invention
The present invention relates to a centrifugal fan that is suitable for use as, for example, a fan of an air-conditioning system for vehicles.
2. Description of Related Art
Heating, ventilation, and air-conditioning (HVAC) units are widely used in air-conditioning systems for vehicles. A fan included in such an HVAC unit is, for example, a centrifugal fan. When a centrifugal fan including an impeller with a shroud is used as the centrifugal fan, a space is unavoidably provided between the shroud and a casing wall facing the shroud. A pressure difference is generated in this space by a pressurized main flow at the outlet side of the impeller, resulting in the generation of a leakage flow that flows against the main flow. This leakage flow causes not only a decrease in the efficiency of the fan but also noise when the leakage flow is combined with the main flow again.
According to Publication of Japanese Patent No. 3351438, in order to suppress such a leakage flow, the above space is formed so as to have a uniform dimension from the outer peripheral side to the inner peripheral side of the shroud.